The Latin word Pontifex means “high priest” or “chief priest”. The word is supposedly derived from the Latin words for “bridge” and “maker”, but the Oxford English Dictionary says that this may be only a ‘folk etymology’. In any case, when used in Latin, the word ‘pontifex’ means high priest. It is never used in Latin to refer to someone who builds bridges!

In ancient Rome, the term pontifex and the plural pontifices were used to refer to a council of 5 Roman (pagan) priests. Each priest was a pontifex, and the head of the council was the Pontifex Maximus. But all of the pontifices has roles of leadership over the other priests.

The word “pontifex” also occurs numerous times in the Old Testament, to refer to the Jewish high priest. It is used in John’s Gospel to refer to the Jewish high priests (plural: pontifices). And it is used in The Letter to the Hebrews to refer to Jesus:

[Hebrews]
{6:20} ubi præcursor pro nobis introivit Iesus, secundum ordinem Melchisedech Pontifex factus in æternum.
{6:20} to the place where the forerunner Jesus has entered on our behalf, so as to become the High Priest for eternity, according to the order of Melchizedek.

The exact phrase “pontifex maximus” does not occur in the Bible, but there is a related use of both terms:

[Leviticus]
{21:10} Pontifex, id est, sacerdos maximus inter fratres suos, super cuius caput fusum est unctionis oleum, et cuius manus in sacerdotio consecratæ sunt, vestitusque est sanctis vestibus, caput suum non discooperiet, vestimenta non scindet:
{21:10} The high priest, that is, the priest who is the greatest among his brothers, upon whose head the oil of anointing has been poured, and whose hands have been consecrated for the priesthood, and who has been vested with the holy vestments: he shall not expose his head; he shall not rend his vestments.

The high priest (pontifex) is the greatest (maximus) of all his brethren priests and bishops. The Pope is the Pontifex, because he is the High Priest of the Church, the Vicar of Christ, whose authority is from Christ. Only Jesus Christ is the one true High Priest. All other priests are only true priests by their association with Him.

The Pope is called Maximus because he is the leader of the other ‘chief priests’, the Bishops of the Church. The Pope is also called Maximus because the Pontifex of the one holy Catholic Church is much greater than the pagan high priests of Rome and greater even than the Jewish high priests of ancient times.

So the Twitter name used by Pope Benedict XVI means “high priest”. It does not mean “bridge builder”.

By the way, the abbreviation PP., as in: ‘Benedict PP. XVI’, simply means Pope. The word for Pope in Latin and Greek, just as in English, uses the letter P twice. That’s all it means.